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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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CHTLDS GLACIER
401
VABIATIONS m WIDTH OP COPPER RIVER IN FBONT OF CHUJDS GLACIER FBOM 1900
TO 1909
Date	Width of River	Based on Maps by
October 9, 1900	About 1600 feet	D. C. Witherspoon
November, 1905	1100-1650    "	Railway Survey
Summer,    1906	About 1600    "	U. S. Geol. Survey
August 24, 1907	1275-1750     "	Railway Survey
Summer,    1908	1000-1800     "	((                          CC
Spring,       1909	625-1125     "	                  cc
July,           1909	775-1300     "	((                          CC
During this period of advance, in 1909, the ice motion was about four feet or more per day near the moraine-covered northern margin of Childs Glacier. Nearer the glacier margin, just north of the point of observation (a, Figi 57) the terminus of the glacier had no appreciable motion; at least the edge did not move forward, for small shrubs still grew upon it, as they had done from 1900 to 1909.
The determination of the rate of motion in 1909, recorded above, is the work of A. O. Johnson, one of the railway engineers, who made instrumental observations for two weeks, which he has kindly given us permission to publish.1 He used a baseline 2983.7 feet long and made transit readings upon a piece of gas pipe 5 feet long driven into the ice, with a flag on top of it. These 1909 observations show the following movement :
RATH OF MOVEMENT IN CHILDS GLACIER IN JULY, 1909
July 15,   8 a.m. to July 16,   3 p.m.
If inches per hour.
cc	16,	3 p.m.	cc	cc	18,	7	a.m.	2	(C	cc          cc
<	18,	7 a.m.	(C	cc	20,	1	p.m.	If		cc           cc
<c	20,	1 p.m.	(C		23,	12	noon	If	<(	cc           cc
cc	23,	12 noon		cc	25,	8	a.m.	2A	"	cc           cc
<(	25,	8 a.m.	cc	cc	30,	8	a.m.	*&	cc	cc           cc
The average of two weeks' observations is, therefore, a little less than 2 inches an hour, or 45 inches a day. Mr. Johnson says that the rate of movement at this point was slower than that in the middle of the glacier, and we assume that in mid-glacier it may have been as much as 6 feet a day.
The rate of melting of the surface of Childs Glacier during the summer of 1909, may be computed from the fact that the gas pipe holding Mr. Johnson's flag, and which was drilled into a flat surface to a depth of 3 feet, had to be reset every 5 days from July 15 to 30, because the surrounding, ice melted to the bottom of the drilled hole. This would give a mim'Tmim rate of melting of a little over 7 inches per day.
Mr. Johnson estimated that the amount and rate of discharge of icebergs in 1909 was about twice as great as in 1908, and he states that the iceberg waves began to cut far
1 Personal communication, Feb. 12, 1910. 26